High-temperature organic working fluids have been introduced as the working fluids in power plants and as working and heat transfer intermediates in order to overcome the short comings of the use of the water steam medium used for heat transfer or for waste heat recovery and power generation. Heat-energy converters, based on the thermodynamic Organic Rankine Cycle, or similar heat-energy transfer systems, are useful in heat recovery and power generation in particular in remote locations, where the heat is derived from various sources, such as gas turbine exhaust gases, combustion of conventional fuels, combustion of biomass fuels, geothermal sources, solar heat collectors and waste heat in power plants and other industrial processes, for the purpose of producing electrical power in the range of from a hundred or more Watts (W) and up to a few of tens Megawatts (MW). Organic fluids sustainable at temperatures as high as about 350° C. are advantageous over water steam, and can be successfully utilized in power generation cycles even at low condensing temperatures and high turbine expansion ratios where the use of steam may be limited due to formation of liquid droplets at the turbine outlet due to the expansion of the steam which may cause erosion to the turbine blades. Because of the nature of the organic fluids they become superheated (or dry) in the expansion process a characteristic which prevents the formation of liquid droplets as is the case with steam. Organic fluids and their derivatives operable under a range of relatively low temperatures normally up to about 200° C. are CFCs, Freon, butane including n-butane and iso-butane, and pentane, also including the n-pentane and iso-pentane isomers. For applications where higher operating temperatures are required a transition was required to aromatic hydrocarbons, alkylated aromatic hydrocarbons, fluorinated hydrocarbons such as F75 and F43 and silicone based oils. Examples for alkylated aromatic hydrocarbons are commercial Dowtherm J, which is a mixture of isomers of alkylated aromatic hydrocarbon manufactured by the flow Chemical Company and Therminol LT, an alkyl substituted aromatic hydrocarbon, manufactured by the Solutia Inc.
The use of the above-mentioned working fluids does have, however, several drawbacks. First, fluids such as F75 or F43 are expensive. Second, such working fluids require periodic treatment and recycling. Third, they limit operating temperatures resulting in lower efficiency.
There is, therefore, a need for a stable, commercially available organic compound, which can be operated in its liquid and vapor states in a wide range of temperatures, thus successfully exhibiting improved performance as a working fluid or thermal fluid for either power or electricity generating cycles, or heat transfer cycle.
It is therefore an object of the present invention to provide a highly thermally stable fluid useful as a working fluid for power or electricity generating cycles or as a heat transfer fluid or heat transfer cycles, or both.
It is another object of the present invention to provide a working fluid that has a high critical temperature and relatively low pressures at elevated temperatures.
It is another object of the present invention to provide a working fluid that has a high auto-ignition temperature.
It is another object of the present invention to provide a working fluid that has a flow freezing or solidification temperature.
It is still another object of the present invention to provide a working fluid that is benign to humans and to the environment.
It is still another object of the present invention to provide a working fluid that can be easily obtainable by those in the art.
It is still another object of the present invention to provide a working fluid that is operable in a wide range of temperatures.
It is still another object of the present invention to provide a working fluid for use in an organic Rankine cycle electricity or power production in heat recovery applications or other heat-energy conversion cycles, and/or as a heat transfer fluid in heat transfer cycles.
It is still another object of the present invention to provide a use of such a working fluid for heat and waste heat recovery from various heat sources for electricity or power generation and/or others usage of the heat.
These and other objects of the present invention will become clear as the description proceeds.